Friday, October 22, 2010

Create a vista Gadget

Got my Windows 7 box in both home and office. It is time to play the Gadget side bar!

As a start project, I want to create a gadget to monitor a web site. Whenever it changes, it will display different icon. So you need a html file, a xml configuration file, and a javascript.

(1) How to access the Internet?
There are two ways: XMLHTTPRequest or create a dll to wrap the logic inside. Here I use the first approach.

(2) The regular request seems never sent out
It is because of the cache. Add the header like:
xmlhttp.setRequestHeader("If-Modified-Since", "Sat 1 Jan 2000 00:00:00 GMT");

(3) How to detect the network connection error
You can hook a timeout. Or if simply the web server did not start up, you will get the status code 12029 (WinInet error of the attmpt to connection to the server failed).

(4) I use:
<body onload="start();windows.setInterval('refresh()',5000)" ....>
to request the web site every 5 seconds.

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